Additional file 1:
This video showed part of major procedures mentioned in the study as follows: First, three-dimensional images of the ankle were extracted by 3-D interactive and automatic segmentation technique after SSD reconstruction, and the color of labeled bones gradually turned pink (talus), silvery (fibula) and green (tibia). Second, the measuring plane (called plane Y in the text) was selected individually. The talus was hided and the distal tibia articular surface was clicked to create a pseudo-straighten plane as the tibial plafond (called plane X in the text). “Point A” was selected on the anterior tubercle, which was defined as the intersection of the tangential along the anterior and posterior tubercle. The plane via point A paralleling the tibial plafond (plane X) was described as the measuring plane. The perpendicular distance between two planes was measured. At last, after reference points were conformed, measurements for some parameters were carried out. For example, the posterior tibiofibular clear space (TCS-P) was measured in the 3-D image, as well as in the 2D axial image of CT scans as control. In the 3-D image, the clear space of the posterior tibiofibular at the level of plane Y was captured expediently for further measurement. TCS-P in the 2-D axial images was measured in multiple planar reconstruction (MPR) images at the same level of the measuring plane. (MP4 16470 kb)